Zoom optical system and electronic imaging apparatus using the same

ABSTRACT

A zoom optical system has, in order from the object side, a first lens unit with negative refracting power, including one biconcave-shaped lens component, a second lens unit with positive refracting power, a third lens unit with negative refracting power, and a fourth lens unit with positive refracting power. When the magnification of the zoom optical system is changed, relative distances between individual lens units are varied and the zoom optical system satisfies the following condition: 
       0.2≦ d   CD   /fw ≦1.2 
     where d CD  is spacing between the third lens unit and the fourth lens unit on the optical axis in infinite focusing at a wide-angle position and fw is the focal length of the entire system of the zoom optical system at the wide-angle position.

This application claims benefits of Japanese Application No. 2006-316190filed in Japan on Nov. 22, 2006, the contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a zoom optical system which is peculiarlysuitable for an electronic imaging optical system, has a large aperture,and is excellent in imaging performance and an electronic imagingapparatus having this zoom optical system.

2. Description of Related Art

Digital cameras have reached levels of practical use in high pixeldensity (high image quality) and small-sized and slim designs. As aresult, the digital cameras have replaced silver-halide 35 mm cameraswith respect to their functions and markets. The next performancerequirement is that an object can be clearly photographed even insurroundings in which the amount of light is small. Hence, it isimperatively needed that high imaging performance and small thicknessthat have been attained so far in optical systems are left as they areand a large aperture ratio is designed.

As a conventional zoom optical system suitable for the design of thelarge aperture ratio, for example, a positive refracting power lead typezoom optical system has been known. This positive refracting power leadtype zoom optical system includes, in order from the object side, afirst lens unit with positive refracting power, a second lens unit withnegative refracting power, a third lens unit with positive refractingpower, and a fourth lens unit with positive refracting power.

On the other hand, as a zoom optical system suitable for a slim design,for example, a negative refracting power lead type zoom optical systemhas been known. This negative refracting power lead-type zoom opticalsystem includes, in order from the object side, a first lens unit withnegative refracting power, a second lens unit with positive refractingpower, and a third lens unit with positive refracting power. In thenegative refracting power lead type zoom optical system, the first lensunit is constructed with a plurality of lens components in order tocorrect aberration.

Also, in the negative refracting power lead type zoom optical system, asan example where there is the possibility of a slimmer design, the firstlens unit is constructed with only one lens component to adopt aremarkable arrangement in view of the slim design.

SUMMARY OF THE INVENTION

The zoom optical system according to the present invention comprises, inorder from the object side, a lens unit A with negative refractingpower, including one biconcave-shaped lens component, a lens unit B withpositive refracting power, a lens unit C with negative refracting power,and a lens unit D with positive refracting power. When the magnificationof the zoom optical system is changed, relative distances betweenindividual lens units are varied and the zoom optical system satisfiesthe following condition:

0.2≦d _(CD) /fw≦1.2  (1)

where d_(CD) is spacing between the lens unit C and the lens unit D onthe optical axis in infinite focusing at a wide-angle position and fw isthe focal length of the entire system of the zoom optical system at thewide-angle position.

In the zoom optical system of the present invention, it is desirablethat the lens unit A includes a cemented lens component of a positivelens L_(AP) and a negative lens L_(AN), and the positive lens L_(AP) ismade of energy curing resin and is configured directly on the negativelens L_(AN).

In the zoom optical system of the present invention, it is desirablethat the cemented lens component of the lens unit A includes, in orderfrom the object side, the negative lens L_(AN) and the positive lensL_(AP).

In the zoom optical system of the present invention, it is desirablethat when z is taken as the coordinate in the direction of the opticalaxis, h is taken as the coordinate normal to the optical axis, krepresents a conic constant, A₄, A₆, A₈, and A₁₀ represent asphericalcoefficients, R represents the radius of curvature of a sphericalcomponent on the optical axis, and the configuration of an asphericalsurface is expressed by the following equation:

$\begin{matrix}{z = {\frac{h^{2}}{R\left\lbrack {1 + \left\{ {1 - {\left( {1 + k} \right){h^{2}/R^{2}}}} \right\}^{1/2}} \right\rbrack} + {A_{4}h^{4}} + {A_{6}h^{6}} + {A_{8}h^{8}} + {A_{10}h^{10}} + \ldots}} & (2)\end{matrix}$

the zoom optical system satisfies the following condition:

0.1≦|z _(AR)(h)−z _(AC)(h)/tp≦0.96  (3)

where z_(AC) is the shape of the cementation-side surface, according toEquation (2), of the positive lens L_(AP); z_(AR) is the shape of theair-contact-side surface, according to Equation (2), of the positivelens L_(AP); h is expressed by h=0.7 fw when the focal length of theentire system of the zoom optical system at the wide-angle position isdenoted by fw; tp is the thickness, measured along the optical axis, ofthe positive lens L_(AP), and always Z (0)=0.

In the zoom optical system of the present invention, it is desirablethat when z is taken as the coordinate in the direction of the opticalaxis, h is taken as the coordinate normal to the optical axis, krepresents a conic constant, A₄, A₆, A₈, and A₁₀ represent asphericalcoefficients, R represents the radius of curvature of a sphericalcomponent on the optical axis, and the configuration of an asphericalsurface is expressed by the following equation:

$\begin{matrix}{z = {\frac{h^{2}}{R\left\lbrack {1 + \left\{ {1 - {\left( {1 + k} \right){h^{2}/R^{2}}}} \right\}^{1/2}} \right\rbrack} + {A_{4}h^{4}} + {A_{6}h^{6}} + {A_{8}h^{8}} + {A_{10}h^{10}} + \ldots}} & (2)\end{matrix}$

the zoom optical system satisfies the following conditions:

−50≦k _(AF)≦10  (5)

−20≦k _(AR)≦20  (6)

and further satisfies the following condition:

−8≦z _(AF)(h)/z _(AR)(h)≦2  (7)

where k_(AF) is a k value relative to the most object-side surface ofthe lens unit A and k_(AR) is a k value relative to the most image-sidesurface of the lens unit A, each of which is the k value in Equation(2); z_(AF) is the shape of the most object-side surface of the lensunit A; z_(AR) is the shape of the most image-side surface of the lensunit A; and h is expressed by h=0.7 fw when the focal length of theentire system of the zoom optical system at the wide-angle position isdenoted by fw.

In the zoom optical system of the present invention, it is desirablethat a refractive index ndp of the positive lens L_(AP), relative to thed line, satisfies the following condition:

1.50≦ndp≦1.85  (8)

In the zoom optical system of the present invention, it is desirablethat when the magnification is changed in the range from the wide-angleposition to a telephoto position, the lens unit A is moved back andforth along the optical axis in such a way that the lens unit A isinitially moved toward the image side.

In the zoom optical system of the present invention, it is desirablethat the lens unit B includes two lens components, a single lenscomponent and a cemented lens component, or three lenses.

In the zoom optical system of the present invention, it is desirablethat the negative lens unit C and the positive lens unit D in which amutual spacing is variable are arranged on the image side of the lensunit B.

In the zoom optical system of the present invention, it is desirablethat the lens unit C includes the negative lens alone and the lens unitD includes the positive lens alone.

In the zoom optical system of the present invention, it is desirablethat a distance along the optical axis between the lens unit A and thelens unit B is varied for the purpose of changing the magnification; anegative lens component of the lens unit A includes a cemented lens ofthe positive lens L_(AP) and the negative lens L_(AN); and in anorthogonal coordinate system in which the axis of abscissas is taken asvdp and the axis of ordinates is taken as θgFp, when a straight lineexpressed by

θgFp=αp×vdp+βp(where αp=−0.00163)

is set, vdp and θgFp of the positive lens L_(AP) are contained in boththe region defined by a straight line in the lower limit of Condition(11) described below and by a straight line in the upper limit ofCondition (11) and the region defined by Condition (12) described below:

0.6400<βp<0.9000  (11)

3<vdp<27  (12)

where θgFp is a partial dispersion ratio (ng−nF)/(nF−nC) of the positivelens L_(AP), vdp is an Abbe's number (nd−1)/(nF−nC) of the positive lensL_(AP), nd is a refractive index relative to the d line, nC is arefractive index relative to the C line, nF is a refractive indexrelative to the F line, and ng is a refractive index relative to the gline.

In the zoom optical system of the present invention, it is desirablethat in an orthogonal coordinate system in which the axis of abscissasis taken as vdp and the axis of ordinates is taken as θhgp, when astraight line expressed by

θhgp=αhgp×vdp+βhgp(where αhgp=−0.00225)

is set, vdp and θhgp of the positive lens L_(AP) are contained in boththe region defined by a straight line in the lower limit of Condition(13) described below and by a straight line in the upper limit ofCondition (13) and the region defined by Condition (12) described below.

0.5700<βhgp<0.9500  (13)

3<vdp<27  (12)

where θhgp is a partial dispersion ratio (nh−ng)/(nF−nC) of the positivelens L_(AP), vdp is an Abbe's number (nd−1)/(nF−nC) of the positive lensL_(AP), nd is a refractive index relative to the d line, nC is arefractive index relative to the C line, nF is a refractive indexrelative to the F line, ng is a refractive index relative to the g line,and nh is a refractive index relative to the h line.

In the zoom optical system of the present invention, it is desirable tosatisfy the following condition:

0.08≦θgFp−θgFn≦0.50  (14)

where θgFp is a partial dispersion ratio (ng−nF)/(nF−nC) of the positivelens L_(AP), θgFn is a partial dispersion ratio (ng−nF)/(nF−nC) of thenegative lens L_(AN), nC is a refractive index relative to the C line,nF is a refractive index relative to the F line, and ng is a refractiveindex relative to the g line.

In the zoom optical system of the present invention, it is desirable tosatisfy the following condition:

0.09≦θhgp−θhgn≦0.60  (15)

where θhgp is a partial dispersion ratio (nh−ng)/(nF−nC) of the positivelens L_(AP), θhgn is a partial dispersion ratio (nh−ng)/(nF−nC) of thenegative lens L_(AN), nC is a refractive index relative to the C line,nF is a refractive index relative to the F line, ng is a refractiveindex relative to the g line, and nh is a refractive index relative tothe h line.

In the zoom optical system of the present invention, it is desirable tosatisfy the following condition:

vdp−vdn≦−30  (16)

where vdp is an Abbe's number (nd−1)/(nF−nC) of the positive lensL_(AP), vdn is an Abbe's number (nd−1)/(nF−nC) of the negative lensL_(AN), nd is a refractive index relative to the d line, nC is arefractive index relative to the C line, and nF is a refractive indexrelative to the F line.

The electronic imaging apparatus having the zoom optical systemaccording to the present invention comprises a zoom optical system andan electronic imaging unit that has an electronic image sensor in theproximity of the imaging position of the zoom optical system so that animage formed through the zoom optical system is picked up by theelectronic image sensor and image data picked up by the electronic imagesensor are electrically processed and can be output as image data whoseformat is changed. The zoom optical system is the zoom optical system ofthe present invention described above, and in nearly infinite objectpoint focusing, satisfies the following condition:

0.7<y ₀₇/(fw·tan ω_(07w))<0.94  (19)

where y₀₇ is expressed by y₀₇=0.7y₁₀ when y₁₀ denotes a distance fromthe center to a point farthest from the center (the maximum imageheight) within an effective imaging surface (an imageable surface) ofthe electronic image sensor, ω_(07w) is an angle made by a direction ofan object point corresponding to an image point, connecting the centerof the imaging surface at the wide-angle position and the position ofthe image height y₀₇, with the optical axis, and fw is the focal lengthof the entire system of the zoom optical system at the wide-angleposition.

When the first lens unit is constructed with only one lens component indesigning the large aperture ratio of the optical system, astigmatism isliable to deteriorate. According to the present invention, even when thefirst lens unit is constructed with only one lens component, astigmatismcan be favorably corrected. As a result, the zoom optical system of thelarge aperture ratio and the electronic imaging apparatus having thiszoom optical system are attained. Moreover, when the first lens unit isconstructed with only one lens component, the length of a collapsiblelens barrel can be reduced. Whereby, in the zoom optical system, theslim design and the large aperture ratio can be made compatible.

These and other features and advantages of the present invention willbecome apparent from the following detailed description of the preferredembodiments when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are sectional views showing optical arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, in infinite object point focusing of Embodiment1 of the zoom optical system according to the present invention;

FIGS. 2A-2D, 2E-2H, and 2I-2L are diagrams showing aberrationcharacteristics at wide-angle, middle, and telephoto positions,respectively, in infinite object point focusing of the zoom opticalsystem of FIGS. 1A-1C;

FIGS. 3A, 3B, and 3C are sectional views showing optical arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, in infinite object point focusing of Embodiment2 of the zoom optical system according to the present invention;

FIGS. 4A-4D, 4E-4H, and 4I-4L are diagrams showing aberrationcharacteristics at wide-angle, middle, and telephoto positions,respectively, in infinite object point focusing of the zoom opticalsystem of FIGS. 3A-3C;

FIGS. 5A, 5B, and 5C are sectional views showing optical arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, in infinite object point focusing of Embodiment3 of the zoom optical system according to the present invention;

FIGS. 6A-6D, 6E-6H, and 6I-6L are diagrams showing aberrationcharacteristics at wide-angle, middle, and telephoto positions,respectively, in infinite object point focusing of the zoom opticalsystem of FIGS. 5A-5C;

FIGS. 7A, 7B, and 7C are sectional views showing optical arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, in infinite object point focusing of Embodiment4 of the zoom optical system according to the present invention;

FIGS. 8A-8D, 8E-8H, and 8I-8L are diagrams showing aberrationcharacteristics at wide-angle, middle, and telephoto positions,respectively, in infinite object point focusing of the zoom opticalsystem of FIGS. 7A-7C;

FIGS. 9A, 9B, and 9C are sectional views showing optical arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, in infinite object point focusing of Embodiment5 of the zoom optical system according to the present invention;

FIGS. 10A-10D, 10E-10H, and 10I-10L are diagrams showing aberrationcharacteristics at wide-angle, middle, and telephoto positions,respectively, in infinite object point focusing of the zoom opticalsystem of FIGS. 9A-9C;

FIGS. 11A, 11B, and 11C are sectional views showing opticalarrangements, developed along the optical axis, at wide-angle, middle,and telephoto positions, respectively, in infinite object point focusingof Embodiment 6 of the zoom optical system according to the presentinvention;

FIGS. 12A-12D, 12E-12H, and 12I-12L are diagrams showing aberrationcharacteristics at wide-angle, middle, and telephoto positions,respectively, in infinite object point focusing of the zoom opticalsystem of FIGS. 11A-11C;

FIG. 13 is a front perspective view showing the appearance of a digitalcamera incorporating the zoom optical system according to the presentinvention;

FIG. 14 is a rear perspective view showing the digital camera of FIG.13; and

FIG. 15 is a sectional view showing the optical structure of the digitalcamera of FIG. 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before undertaking the description of the embodiments, the function andeffect of the present invention will be explained. The zoom opticalsystem of the present invention comprises, in order from the objectside, a lens unit A with negative refracting power, including onebiconcave-shaped lens component, a lens unit B with positive refractingpower, a lens unit C with negative refracting power, and a lens unit Dwith positive refracting power. When the magnification of the zoomoptical system is changed, relative distances between individual lensunits are varied.

When the lens unit A is constructed with a single lens component alone,it is necessary to render correction for astigmatism severe withenlarging aperture ratio. Hence, the zoom optical system of the presentinvention is constructed so that the spacing d_(CD) between the lensunit C and the lens unit D on the optical axis in infinite focusing at awide-angle position satisfies the following condition. Whereby,astigmatism produced at the wide-angle position is corrected whichformerly have been not completely corrected in the lens unit A includingthe single lens component alone.

0.2≦d _(CD) /fw≦1.2  (1)

where fw is the focal length of the entire system of the zoom opticalsystem at the wide-angle position.

Below the lower limit of Condition (1), it becomes particularlydifficult to make favorable correct for astigmatism at the wide-angleposition. Alternatively, it becomes difficult to lower a sensitivity todecetration in each of the lens units C and D. On the other hand, beyondthe upper limit of Condition (1), it becomes difficult to reduce thelength of the lens barrel when collapsed. Also, when the lens unit A isconstructed with the single lens component alone, this arrangement isvery effective for the slim design in a depth direction of the opticalsystem. In particular, when the collapsible lens barrel is adopted, thegreatest effect is brought about.

Instead of satisfying Condition (1), it is more favorable to satisfy thefollowing condition:

0.25≦d _(CD) /fw≦0.9  (1′)

Further, instead of satisfying Condition (1), it is most favorable tosatisfy the following condition:

0.3≦d _(CD) /fw≦0.6  (1″)

In order to design the large aperture ratio, it is good practice toconfigure the lens unit A as a cemented lens component of the positivelens L_(AP) and the negative lens L_(AN). It is desirable that anorganic material such as resin, for example, energy curing resin, isused as the optical material of the positive lens L_(AP), which isconfigured directly on the negative lens L_(AN). In such a way, it ispossible to work (configure) as thin the positive lens L_(AP) aspossible. As the energy curing resin, for example, ultraviolet curingresin is available. Also, the fact that the lens unit A is constructedwith the single lens component is favorable for the slim design of theoptical system. It is rather desirable that the cemented lens componentof the lens unit A includes, in order from the object side, the negativelens L_(AN) and the positive lens L_(AP). It is said that this isfavorable from the viewpoint of durability of the resin.

It is desirable that a lens shape is taken as described below. When z istaken as the coordinate in the direction of the optical axis, h is takenas the coordinate normal to the optical axis, k represents a conicconstant, A₄, A₆, A₈, and A₁₀ represent aspherical coefficients, and Rrepresents the radius of curvature of a spherical component on theoptical axis, the configuration of an aspherical surface is expressed bythe following equation:

$\begin{matrix}{z = {\frac{h^{2}}{R\left\lbrack {1 + \left\{ {1 - {\left( {1 + k} \right){h^{2}/R^{2}}}} \right\}^{1/2}} \right\rbrack} + {A_{4}h^{4}} + {A_{6}h^{6}} + {A_{8}h^{8}} + {A_{10}h^{10}} + \ldots}} & (2)\end{matrix}$

In this case, it is desirable to satisfy the following condition:

0.1≦|z _(AR)(h)−z _(AC)(h)/tp≦0.96  (3)

where z_(AC) is the shape of the cementation-side surface of thepositive lens L_(AP) and z_(AR) is the shape of the air-contact-sidesurface of the positive lens L_(AP), both according to Equation (2); his expressed by h=0.7 fw when the focal length of the entire system ofthe zoom optical system at the wide-angle position is denoted by fw; andtp is the thickness, measured along the optical axis, of the positivelens L_(AP). Also, always Z (0)=0.

Below the lower limit of Condition (3), correction for chromaticaberration is liable to become insufficient. On the other hand, beyondthe upper limit of Condition (3), it becomes difficult to ensure aperipheral edge thickness of the positive lens L_(AP). Specifically,when the thickness of the positive lens L_(AP) is made small, it isnecessary to ensure the peripheral edge thickness by a preset amount,but it becomes difficult to ensure this preset amount of edge thickness.

Instead of satisfying Condition (3), it is more desirable to satisfy thefollowing condition:

0.3≦|z _(AR)(h)−z _(AC)(h)/tp≦0.94  (3′)

Further, instead of satisfying Condition (3), it is most desirable tosatisfy the following condition:

0.5≦|z _(AR)(h)−z _(AC)(h)/tp≦0.92  (3″)

When the thickness, measured along the optical axis, of the negativelens L_(AN) of the lens unit A is denoted by tn, it is favorable tosatisfy the following condition:

0.3≦tp/tn≦1.3  (4)

Alternatively, when shapes of the most object-side surface and the mostimage-side surface of the lens unit A are considered as described below,astigmatism can be effectively corrected.

That is, when the configuration of the aspherical surface is expressedby Equation (2), it is desirable to satisfy the following conditions:

−50≦k _(AF)≦10  (5)

−20≦k _(AR)≦20  (6)

and to further satisfy the following condition:

−8≦z _(AF)(h)/z _(AR)(h)≦2  (7)

where k_(AF) is a k value relative to the most object-side surface ofthe lens unit A and k_(AR) is a k value relative to the most image-sidesurface of the lens unit A, each of which is the k value in Equation(2); z_(AF) is the shape of the most object-side surface of the lensunit A; z_(AR) is the shape of the most image-side surface of the lensunit A; and h is expressed by h=0.7 fw when the focal length of theentire system of the zoom optical system at the wide-angle position isdenoted by fw.

Beyond the upper limit of Condition (7), this is liable to becomedisadvantageous to correction for astigmatism. On the other hand, belowthe lower limit of Condition (7), the amount of occurrence of distortionis materially increased. Hence, even though an image processing functionto be described later is used to correct distortion, an image peripheryis enlarged radially (in a direction from the image center toward theperiphery) by this correction. As a consequence, the resolution of aperipheral portion in a meridional direction is liable to be impaired.

Instead of satisfying Condition (7), it is more desirable to satisfy thefollowing condition:

−4≦z _(AF)(h)/z _(AR)(h)≦0  (7′)

Further, instead of satisfying Condition (7), it is most desirable tosatisfy the following condition:

−2≦z _(AF)(h)/z _(AR)(h)≦−0.3  (7″)

When a refractive index ndp relative to the d line of the positive lensL_(AP) (the optical material used for the positive lens L_(AP)) of thelens unit A satisfies the following condition, this is advantageous tocorrection for astigmatism.

1.50≦ndp≦1.85  (8)

Below the lower limit of Condition (8), astigmatism is not completelycorrected. On the other hand, beyond the upper limit of Condition (8),coma is not completely corrected.

Instead of satisfying Condition (8), it is more desirable to satisfy thefollowing condition:

1.55≦ndp≦1.80  (8′)

Further, instead of satisfying Condition (8), it is most desirable tosatisfy the following condition:

1.57≦ndp≦1.77  (8″)

Also, in the zoom optical system of the present invention, it isfavorable that when the magnification is change in the range from thewide-angle position to the telephoto position, the lens unit A is movedback and forth along the optical axis in such a way that it is initiallymoved toward the image side. This causes the overall length of theoptical system to be reduced and is effective for the slim design wherethe lens barrel is collapsed. Also, when the optical system is designedfor the large aperture ratio, for example, when the F value of theoptical system is made smaller than F/2.8, it is desirable thatastigmatism which is liable to occur when the lens unit A is constructedwith the single lens component alone is previously corrected by the lensunits other than the lens unit A.

Thus, in the present invention, in order to make favorable correctionsfor chromatic aberration and astigmatism, the lens unit B is constructedwith two lens components, a single lens component and a cemented lenscomponent, or three lenses. Here, it is desirable that the lens unit Bhas positive refracting power and includes, in order from the objectside, a single positive lens component B1 and a cemented lens componentB2 of a positive lens and a negative lens. Alternatively, it isdesirable that the lens unit B has positive refracting power andincludes the single positive lens component B1 and the cemented lenscomponent B2 of a positive lens, a negative lens, and a negative lens.

In such an arrangement, it is desirable that an average value_(AVE)nd_(2p) of refractive indices (relative to the d line) of allpositive lenses in the lens component B1 and the lens component B2 is1.81 or more. By doing so, astigmatism can be favorably corrected. Also,if the average value _(AVE)nd_(2p) is below 1.81, it becomes difficultthat astigmatism is favorably corrected.

It is also desirable that, from the viewpoint of chromatic aberration,an average value _(AVE)vd_(2N) of Abbe's numbers (relative to the dline) of all negative lenses in the lens component B1 and the lenscomponent B2 is 25 or less (preferably 10 or more). Alternatively, inthe zoom optical system of the present invention, it is desirable thattwo lenses, the negative lens unit C and the positive lens unit D, inwhich a mutual spacing is variable are arranged on the image side of thelens unit B. By doing so, even when the large aperture ratio (forexample, brightness below F/2.8) is obtained at the wide-angle position,it becomes possible to correct astigmatism at an adequate level in theentire region of zooming and focusing. It is particularly desirable thatwhen the magnification is changed in the range from the wide-angleposition to the telephoto position, the lens unit C and the lens unit Dare moved while simply widening the relative spacing. Alternatively, itis desirable that the lens unit C and the lens unit D are moved togetherso that the lens unit D approaches an imaging point. Whereby, thefluctuation of astigmatism at the wide-angle position or in themagnification change can be suppressed.

It is also desirable that, in focusing, the lens unit C and the lensunit D are moved while changing the mutual spacing. By doing so, thefluctuation of astigmatism due to focusing can be kept to a minimum. Inparticular, it is desirable that the lens unit C and the lens unit D aremoved so as to narrow the mutual spacing as focusing is performed at ashort distance in a state where the lens unit A and the lens unit B arefixed. Whereby, the fluctuation of astigmatism due to focusing can bekept to a minimum.

In general, one lens unit is placed on the image side of the lens unitB, whereas in the present invention, two lens units are arranged.Therefore, the thickness where the lens barrel is collapsed is increasedfor one lens unit. Thus, in order to check an increase in thickness asfar as possible, it is desirable to take account of the followingdescription:

a. the lens unit C is constructed with a negative lens alone and thelens unit D is constructed with a positive lens alone, and

b. the lens unit C and the lens unit D are designed to satisfy thefollowing conditions:

−1.5≦(R _(CF) +R _(CR))/(R _(CF) −R _(CR))≦1.5  (9)

0.0≦(R _(DF) +R _(DR))/(R _(DF) −R _(DR))≦1.5  (10)

where R_(CF) and R_(DF) are radii of curvature of the most object-sidesurfaces of the lens units C and D, respectively, and R_(CR) and R_(DR)are radii of curvature of the most image-side surfaces of the lens unitsC and D, respectively.

By doing so, dead space between the lens unit B, the lens unit C, andthe lens unit D when the lens barrel is collapsed can be kept to aminimum. Also, when the lens surface is configured as an asphericalsurface, each of R_(CF), R_(CR), R_(DF), and R_(DR) denotes a paraxialradius of curvature. Instead of satisfying Conditions (9) and (10), itis more desirable to satisfy the following conditions:

−1.2≦(R _(CF) +R _(CR))/(R _(CF) −R _(CR))≦1.2  (9′)

0.3≦(R _(DF) +R _(DR))/(R _(DF) −R _(DR))≦1.2  (10′)

Further, instead of satisfying Conditions (9) and (10), it is mostdesirable to satisfy the following conditions:

−1.0≦(R _(CF) +R _(CR))/(R _(CF) −R _(CR))≦1.0  (9″)

0.6≦(R _(DF) +R _(DR))/(R _(DF) −R _(DR))≦1.0  (10″)

Also, in this case, it is favorable that a refractive index nd_(4p) ofthe lens unit D relative to the d line is 1.7 or more and an Abbe'snumber vd_(4p) relative to the d line ranges from 20 to 50.

In the design of the large aperture ratio of the optical system, asmentioned above, the present invention is constructed to considercorrection for astigmatism, but it is also necessary to rendercorrection for chromatic aberration severe. As such, it is favorablethat the positive lens L_(AP) (the optical material used for thepositive lens L_(AP)) of the lens unit A satisfies conditions describedbelow. That is, in an orthogonal coordinate system in which the axis ofabscissas is taken as vdp and the axis of ordinates is taken as θgFp, itis desirable that when a straight line expressed by

θgFp=αp×vdp+βp(where αp=−0.00163)

is set, vdp and θgFp of the positive lens L_(AP) are contained in boththe region defined by a straight line in the lower limit of Condition(11) described below and by a straight line in the upper limit ofCondition (7) and the region defined by Condition (12) described below.

0.6400<βp<0.9000  (11)

3<vdp<27  (12)

where θgFp is a partial dispersion ratio (ng−nF)/(nF−nC) of the positivelens L_(AP), vdp is an Abbe's number (nd−1)/(nF−nC) of the positive lensL_(AP), nd is a refractive index relative to the d line, nC is arefractive index relative to the C line, nF is a refractive indexrelative to the F line, and ng is a refractive index relative to the gline.

Below the lower limit of Condition (11), chromatic aberration due to thesecondary spectrum, namely chromatic aberration of the g line in thecase of achromatism at the F line and the C line, is not completelycorrected when the optical system is designed for the large apertureratio. Consequently, when the object is photographed by the opticalsystem, it is difficult to ensure sharpness of the image of thephotographed object. On the other hand, beyond the upper limit ofCondition (11), chromatic aberration due to the secondary spectrum isovercorrected when the optical system is designed for the large apertureratio. Consequently, like the case of “below the lower limit ofCondition (11)”, it is difficult to ensure sharpness of the image of thephotographed object. Below the lower limit of Condition (12) or beyondthe upper limit of Condition (12), achromatism itself at the F line andthe C line is difficult and the fluctuation of chromatic aberration inzooming is increased, when the optical system is designed for the largeaperture ratio. Hence, when the object is photographed by the opticalsystem, it is difficult to ensure sharpness of the image of thephotographed object.

Instead of satisfying Condition (11), it is more favorable to satisfythe following condition:

0.6800<βp<0.8700  (11′)

Further, instead of satisfying Condition (11), it is much more favorableto satisfy the following condition:

0.6900<βp<0.8200  (11″)

In an orthogonal coordinate system in which the axis of abscissas istaken as vdp and the axis of ordinates is taken as θhgp, it is desirablethat when a straight line expressed by

θhgp=αhgp×vdp+βhgp(where αhgp=−0.00225)

is set, vdp and θhgp of the positive lens L_(AP) are contained in boththe region defined by a straight line in the lower limit of Condition(13) described below and by a straight line in the upper limit ofCondition (13) and the region defined by Condition (12) described below.

0.5700<βhgp<0.9500  (13)

3<vdp<27  (12)

where θhgp is a partial dispersion ratio (nh−ng)/(nF−nC) of the positivelens L_(AP), vdp is an Abbe's number (nd−1)/(nF−nC) of the positive lensL_(AP), nd is a refractive index relative to the d line, nC is arefractive index relative to the C line, nF is a refractive indexrelative to the F line, ng is a refractive index relative to the g line,and nh is a refractive index relative to the h line.

Below the lower limit of Condition (13), chromatic aberration due to thesecondary spectrum, namely chromatic aberration of the h line in thecase of achromatism at the F line and the C line, is not completelycorrected when the optical system is designed for the large apertureratio. Consequently, when the object is photographed by the opticalsystem, purple flare and color blurring are liable to occur in the imageof the photographed object. On the other hand, beyond the upper limit ofCondition (13), chromatic aberration due to the secondary spectrum,namely chromatic aberration of the h line in the case of achromatism atthe F line and the C line, is overcorrected when the optical system isdesigned for the large aperture ratio. Consequently, when the object isphotographed by the optical system, purple flare and color blurring areliable to occur in the image of the photographed object.

Instead of satisfying Condition (13), it is more favorable to satisfythe following condition:

0.6200<βhgp<0.9200  (13′)

Further, instead of satisfying Condition (13), it is much more favorableto satisfy the following condition:

0.6500<βhgp<0.8700  (13″)

In the zoom optical system of the present invention, when the opticalsystem satisfies a condition described below, correction efficiencyrelative to the secondary spectrum is raised where the optical system isdesigned for the large aperture ratio. Consequently, the sharpness ofthe image of the photographed object is increased.

0.08≦θgFp−θgFn≦0.50  (14)

where θgFp is a partial dispersion ratio (ng−nF)/(nF−nC) of the positivelens L_(AP), θgFn is a partial dispersion ratio (ng−nF)/(nF−nC) of thenegative lens L_(AN), nC is a refractive index relative to the C line,nF is a refractive index relative to the F line, and ng is a refractiveindex relative to the g line.

Instead of satisfying Condition (14), it is more desirable to satisfythe following condition:

0.10≦θgFp−θgFn≦0.40  (14′)

Further, instead of satisfying Condition (14), it is most desirable tosatisfy the following condition:

0.12≦θgFp−θgFn≦0.30  (14″)

In the zoom optical system of the present invention, it is desirable tosatisfy a condition described below. In this case, color flare andblurring can be lessened in the image of the photographed object.

0.09≦θhgp−θhgn≦0.60  (15)

where θhgp is a partial dispersion ratio (nh−ng)/(nF−nC) of the positivelens L_(AP), θhgn is a partial dispersion ratio (nh−ng)/(nF−nC) of thenegative lens L_(AN), nC is a refractive index relative to the C line,nF is a refractive index relative to the F line, ng is a refractiveindex relative to the g line, and nh is a refractive index relative tothe h line.

Instead of satisfying Condition (15), it is more desirable to satisfythe following condition:

0.12≦θhgp−θhgn≦0.50  (15′)

Further, instead of satisfying Condition (15), it is most desirable tosatisfy the following condition:

0.15≦θhgp−θhgn≦0.40  (15″)

In the zoom optical system of the present invention, achromatism at theC line and the F line of longitudinal chromatic aberration and chromaticaberration of magnification is facilitated when the optical systemsatisfies the following condition:

vdp−vdn≦−30  (16)

where vdp is an Abbe's number (nd−1)/(nF−nC) of the positive lensL_(AP), vdn is an Abbe's number (nd−1)/(nF−nC) of the negative lensL_(AN), nd is a refractive index relative to the d line, nC is arefractive index relative to the C line, and nF is a refractive indexrelative to the F line.

In stead of satisfying Condition (16), it is more desirable to satisfythe following condition:

vdp−vdn≦−40  (16′)

Further, instead of satisfying Condition (16), it is most desirable tosatisfy the following condition:

vdp−vdn≦−50  (16″)

Next, correction for distortion by image processing will be described indetail.

It is assumed that an infinite object is imaged by an optical systemfree of distortion. In this case, the formed image is free fromdistortion and thus the following equation is established:

f=y/tan ω  (17)

where y is the height of an image point from the optical axis, f is thefocal length of an imaging system, and ω is an angle made by thedirection of an object point corresponding to the image point connectedto the position of the height y from the center of the imaging surfacewith the optical axis.

On the other hand, in the optical system, when barrel distortion istolerated only in the proximity of the wide-angle position, thefollowing condition is obtained:

f>y/tan ω  (18)

That is, when the angle ω and the height y are set to constant values,the focal length f at the wide-angle position may remain long andcorrection for aberration is facilitated accordingly. Although a lensunit corresponding to the lens unit A is usually constructed with atleast two lens components, this reason is that corrections fordistortion and astigmatism are made compatible. In contrast to this, inthe zoom optical system of the present invention, the occurrence ofdistortion is tolerated to some extent. That is, it is not necessarythat corrections for distortion and astigmatism are made compatible, andtherefore the lens unit A can be constructed with only one lenscomponent that is slim.

Thus, the electronic imaging apparatus having the zoom optical system ofthe present invention is such that image data obtained by the electronicimage sensor are processed by the image processing. In this processing,the image data (the image shape) are changed so that barrel distortionis corrected. By doing so, the image data finally obtained provide ashape very similar to the object. Hence, it is only necessary to outputthe image of the object into a CRT and a printer in accordance with theimage data.

Here, it is favorable to adopt the zoom optical system so as to satisfythe following condition in nearly infinite object point focusing:

0.7<y ₀₇/(fw·tan ω_(07w))<0.94  (19)

where y₀₇ is expressed by y₀₇=0.7y₁₀ when y₁₀ denotes a distance fromthe center to a point farthest from the center (the maximum imageheight) within an effective imaging surface (an imageable surface) ofthe electronic image sensor, ω_(07w) is an angle made by a direction ofan object point corresponding to an image point, connecting the centerof the imaging surface at the wide-angle position and the position ofthe image height y₀₇, with the optical axis, and fw is the focal lengthof the entire system of the zoom optical system at the wide-angleposition.

Condition (19) determines the extent of barrel distortion at the zoomwide-angle position. When Condition (19) is satisfied, astigmatism canbe reasonably corrected. Also, a barrel-distorted image isphotoelectrically converted by the image sensor into barrel-distortedimage data. However, in the barrel-distorted image data, a processcorresponding to a change of the image shape is electrically applied byan image processing means that is the signal processing system of theelectronic imaging apparatus. By doing so, even when the image datafinally output from the image processing means are reproduced by adisplay device, distortion is corrected and an image very similar inshape to the object is obtained.

Here, beyond the upper limit of Condition (19), notably in a value closeto 1, distortion is optically well corrected. On the other hand,however, correction for astigmatism becomes difficult, which isunfavorable. Below the lower limit of Condition (19), the proportion ofenlargement of the image periphery in the radial direction is extremelyincreased when image distortion due to distortion of the optical systemis corrected by the image processing means. As a result, the degradationof sharpness of the image periphery becomes pronounced. When Condition(19) is satisfied, favorable correction for astigmatism is facilitatedand the compatibility of the slim design of the zoom optical system withthe design of the large aperture ratio (for example, brightness belowF/2.8 at the wide-angle position) becomes possible.

Instead of satisfying Condition (19), it is more favorable to satisfythe following condition:

0.75<y ₀₇/(fw·tan ω_(07w))<0.93  (19′)

Further, instead of satisfying Condition (19), it is much more favorableto satisfy the following condition:

0.80<y ₀₇/(fw·tan ω_(07w))<0.92  (19″)

In accordance with the drawings, the embodiments of the presentinvention will be explained below. The zoom optical system of each ofthe embodiments of the present invention comprises four lens units. Ofthese lens units, a first lens unit includes two lenses (a cementeddoublet), a second lens unit includes three lenses (a single lens and acemented doublet), a third lens unit includes one lens, and a fourthlens unit includes one lens. Also, the second lens unit may include fourlenses (a single lens and a cemented triplet).

The refracting power of one lens can be imparted to two lenses. In thiscase, although this is not described in the embodiments, one lens can beadded to at least one of the four lens units. In an extreme case, thefirst lens unit includes three lenses, the second lens unit includesfive lenses, the third lens unit includes two lenses, and the fourthlens unit includes two lenses. Also, two lenses may be a cemented lensor separate single lenses (for example, the first lens unit can beconstructed with a cemented doublet and a single lens or with a cementedtriplet). As mentioned above, the zoom optical system is capable ofproviding the first lens unit with two or three lenses, the second lensunit with three to five lenses, the third lenses with one or two lenses,and the fourth lens unit with one or two lenses.

Since one lens is added and thereby the number of lenses used forcorrecting aberration is increased, the design of the large apertureratio is facilitated in a state where aberration is favorably corrected.Moreover, the radius of curvature of each of two lenses can beincreased, and hence the thickness of each lens is not so large. Assuch, the optical system is not oversized.

Embodiment 1

FIGS. 1A, 1B, and 1C are sectional views showing optical arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, in infinite object point focusing of Embodiment1 of the zoom optical system according to the present invention. FIGS.2A-2D, 2E-2H, and 2I-2L are diagrams showing aberration characteristicsat wide-angle, middle, and telephoto positions, respectively, ininfinite object point focusing of the zoom optical system of FIGS.1A-1C. In FIG. 1A, reference symbol I denotes the imaging surface of aCCD that is an electronic image sensor, S denotes an aperture stop, FLdenotes a plane-parallel plate-shaped filter, and CG denotes aplane-parallel plate-shaped CCD cover glass.

The zoom optical system of Embodiment 1 has the lens units, the filterFL, the cover glass CG, and the CCD. (Also, the CCD may or may not beincluded in parts constituting the zoom optical system. The same holdsfor other embodiments.) The zoom optical system comprises, in order fromthe object side, a first lens unit G1 as the lens unit A, the aperturestop S, a second lens unit G2 as the lens unit B, a third lens unit G3as the lens unit C, and a fourth lens unit G4 as the lens unit D.

The first lens unit G1 includes a cemented lens in which a biconcavelens L11 and a positive meniscus lens L12 with a convex surface facingthe object side are cemented, and is constructed with a negative lenscomponent as a whole. The positive meniscus lens L12 with the convexsurface facing the object side is a lens using energy curing resin andis configured on the biconcave lens L11. The second lens unit G2includes a biconvex lens L21 and a cemented lens in which a biconvexlens L22 and a biconcave lens L23 are cemented. The third lens unit G3includes a biconcave lens L31. The fourth lens unit G4 includes abiconvex lens L41.

When the magnification is changed in the range from the wide-angleposition to the telephoto position, the first lens unit G1 is moved backand forth along the optical axis in such a way that the first lens unitG1, after being initially moved toward the image side, is moved towardthe object side. The second lens unit G2 is simply moved, together withthe aperture stop S, along the optical axis toward the object side sothat spacing between the first lens unit G1 and the second lens unit G2is narrowed. The third lens unit G3 is moved back and forth along theoptical axis in such a way that the third lens unit G3 is initiallymoved toward the image side to narrow the spacing between the third lensunit G3 and the fourth lens unit G4 and then is moved toward the objectside. The fourth lens unit G4 is simply moved along the optical axistoward the image side.

Subsequently, numerical data of optical members constituting the zoomoptical system of Embodiment 1 are shown below. In the numerical data ofEmbodiment 1, r₁, r₂, . . . denote radii of curvature of surfaces ofindividual lenses; d₁, d₂, . . . denote thicknesses of individual lensesor air spacings between them; n_(d1), n_(d2), . . . denote refractiveindices of individual lenses at the d line; v_(d1), v_(d2), . . . denoteAbbe's numbers of individual lenses; F denotes the focal length of theentire system of the zoom optical system; and fno denotes the F-numberof the zoom optical system.

Also, when z is taken as the coordinate in the direction of the opticalaxis, h is taken as the coordinate normal to the optical axis, krepresents a conic constant, A₄, A₆, A₈, and A₁₀ represent asphericalcoefficients, and R represents the radius of curvature of a sphericalcomponent on the optical axis, the configuration of an asphericalsurface is expressed by the following equation:

$\begin{matrix}{z = {\frac{h^{2}}{R\left\lbrack {1 + \left\{ {1 - {\left( {1 + k} \right){h^{2}/R^{2}}}} \right\}^{1/2}} \right\rbrack} + {A_{4}h^{4}} + {A_{6}h^{6}} + {A_{8}h^{8}} + {A_{10}h^{10}} + \ldots}} & (2)\end{matrix}$

These symbols are also used for the numerical data of other embodimentsto be described later.

Numerical data 1 r₁ = −13.2566 (aspherical surface) d₁ = 0.8000 n_(d1) =1.49700 ν_(d1) = 81.54 r₂ = 13.1877 d₂ = 0.4237 n_(d2) = 1.63494 ν_(d2)= 23.22 r₃ = 20.8972 (aspherical surface) d₃ = D3 r₄ = ∞ (stop) d₄ =0.3000 r₅ = 8.6234 (aspherical surface) d₅ = 1.8201 n_(d5) = 1.83481ν_(d5) = 42.71 r₆ = −28.1231 (aspherical surface) d₆ = 0.0791 r₇ =7.0624 (aspherical surface) d₇ = 1.7619 n_(d7) = 1.83481 ν_(d7) = 42.71r₈ = −462.1726 d₈ = 0.4000 n_(d8) = 1.80810 ν_(d8) = 24.00 r₉ = 3.9333d₉ = D9 r₁₀ = −34.2928 (aspherical surface) d₁₀ = 0.5000 n_(d10) =1.52542 ν_(d10) = 55.78 r₁₁ = 22.6658 d₁₁ = D11 r₁₂ = 63.7715(aspherical surface) d₁₂ = 1.3800 n_(d12) = 1.83481 ν_(d12) = 42.71 r₁₃= −9.6000 d₁₃ = D13 r₁₄ = ∞ d₁₄ = 0.5000 n_(d14) = 1.54771 ν_(d14) =62.84 r₁₅ = ∞ d₁₅ = 0.5000 r₁₆ = ∞ d₁₆ = 0.5000 n_(d16) = 1.51633ν_(d16) = 64.14 r₁₇ = ∞ d₁₇ = D17 r₁₈ = ∞ (imaging surface) Asphericalcoefficients First surface k = −2.8817 A₂ = 0 A₄ = 0 A₆ = 3.6881 × 10⁻⁶A₈ = −5.5124 × 10⁻⁸ A₁₀ = 0 Third surface k = −2.9323 A₂ = 0 A₄ = 3.6856× 10⁻⁵ A₆ = 5.0066 × 10⁻⁶ A₈ = −5.9251 × 10⁻⁸ A₁₀ = 0 Fifth surface k =−1.8270 A₂ = 0 A₄ = −3.4535 × 10⁻⁴ A₆ = −2.1823 × 10⁻⁵ A₈ = −7.8527 ×10⁻⁸ A₁₀ = 0 Sixth surface k = −5.3587 A₂ = 0 A₄ = −3.7600 × 10⁻⁴ A₆ =−4.8554 × 10⁻⁶ A₈ = −2.1415 × 10⁻⁷ A₁₀ = 0 Seventh surface k = 0.1274 A₂= 0 A₄ = 8.3040 × 10⁻⁵ A₆ = 1.9928 × 10⁻⁵ A₈ = 5.0707 × 10⁻⁷ A₁₀ =8.1677 × 10⁻⁹ Tenth surface k = 57.7596 A₂ = 0 A₄ = −1.7412 × 10⁻⁴ A₆ =−4.6146 × 10⁻⁶ A₈ = 1.1872 × 10⁻⁶ A₁₀ = 0 Twelfth surface k = 0 A₂ = 0A₄ = −4.1049 × 10⁻⁴ A₆ = 3.1634 × 10⁻⁶ A₈ = 0 A₁₀ = 0 Refractive indicesclassified by wavelengths in medium constituting negative lens L_(AN) nd= 1.496999 nC = 1.495136 nF = 1.501231 ng = 1.504507 nh = 1.507205Refractive indices classified by wavelengths in medium constitutingpositive lens L_(AP) nd = 1.634937 nC = 1.627308 nF = 1.654649 ng =1.673790 nh = 1.692286 Zoom data (when D0 (distance from object to firstsurface) is infinite) Wide-angle Middle Telephoto F 6.42002 11.0103118.48954 fno 1.8604 2.4534 3.4040 D0 ∞ ∞ ∞ D3 14.77955 7.26463 2.92947D9 2.20000 6.46215 10.54460 D11 2.38783 2.27230 3.76136 D13 3.167832.30230 1.60000 D17 0.50018 0.50009 0.50003

Embodiment 2

FIGS. 3A, 3B, and 3C are sectional views showing optical arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, in infinite object point focusing of Embodiment2 of the zoom optical system according to the present invention. FIGS.4A-4D, 4E-4H, and 4I-4L are diagrams showing aberration characteristicsat wide-angle, middle, and telephoto positions, respectively, ininfinite object point focusing of the zoom optical system of FIGS.3A-3C. In FIG. 3A, again, reference symbol I denotes the imaging surfaceof a CCD that is an electronic image sensor, S denotes an aperture stop,FL denotes a plane-parallel plate-shaped filter, and CG denotes aplane-parallel plate-shaped CCD cover glass.

The zoom optical system of Embodiment 2 has the lens units, the filterFL, the cover glass CG, and the CCD. The zoom optical system comprises,in order from the object side, a first lens unit G1 as the lens unit A,the aperture stop S, a second lens unit G2 as the lens unit B, a thirdlens unit G3 as the lens unit C, and a fourth lens unit G4 as the lensunit D.

The first lens unit G1 includes a cemented lens in which a biconcavelens L11 and a positive meniscus lens L12 with a convex surface facingthe object side are cemented, and is constructed with a negative lenscomponent as a whole. The positive meniscus lens L12 with the convexsurface facing the object side is a lens using energy curing resin andis configured on the biconcave lens L11. The second lens unit G2includes a biconvex lens L21 and a cemented lens in which a biconvexlens L22 and a biconcave lens L23 are cemented. The third lens unit G3includes a biconcave lens L31. The fourth lens unit G4 includes abiconvex lens L41.

When the magnification is changed in the range from the wide-angleposition to the telephoto position, the first lens unit G1 is moved backand forth along the optical axis in such a way that the first lens unitG1, after being initially moved toward the image side, is moved towardthe object side. The second lens unit G2 is simply moved, together withthe aperture stop S, along the optical axis toward the object side sothat spacing between the first lens unit G1 and the second lens unit G2is narrowed. The third lens unit G3 is simply moved along the opticalaxis toward the object side so that the spacing between the lens unit G3and the lens unit G4 is widened, and the fourth lens unit G4 is movedback and forth along the optical axis in such a way that the fourth lensunit G4 is initially moved toward the object side and then is movedtoward the image side.

Subsequently, numerical data of optical members constituting the zoomoptical system of Embodiment 2 are shown below.

Numerical data 2 r₁ = −14.6626 (aspherical surface) d₁ = 0.8000 n_(d1) =1.58313 ν_(d1) = 59.38 r₂ = 13.6376 d₂ = 0.3515 n_(d2) = 1.70999 ν_(d2)= 15.00 r₃ = 23.8797 (aspherical surface) d₃ = D3 r₄ = ∞ (stop) d₄ =0.3000 r₅ = 8.4853 (aspherical surface) d₅ = 1.7330 n_(d5) = 1.83481ν_(d5) = 42.71 r₆ = −18.3330 (aspherical surface) d₆ = 0.0791 r₇ =8.2088 (aspherical surface) d₇ = 1.5797 n_(d7) = 1.83481 ν_(d7) = 42.71r₈ = −63.5592 d₈ = 0.4000 n_(d8) = 1.80810 ν_(d8) = 23.00 r₉ = 4.3771 d₉= D9 r₁₀ = −53.5288 (aspherical surface) d₁₀ = 0.5000 n_(d10) = 1.85628ν_(d10) = 20.67 r₁₁ = 15.5000 d₁₁ = D11 r₁₂ = 108.2217 (asphericalsurface) d₁₂ = 1.3800 n_(d12) = 1.90000 ν_(d12) = 27.00 r₁₃ = −9.6000d₁₃ = D13 r₁₄ = ∞ d₁₄ = 0.5000 n_(d14) = 1.5477 ν_(d14) = 62.84 r₁₅ = ∞d₁₅ = 0.5000 r₁₆ = ∞ d₁₆ = 0.5000 n_(d16) = 1.51633 ν_(d16) = 64.14 r₁₇= ∞ d₁₇ = D17 r₁₈ = ∞ (imaging surface) Aspherical coefficients firstsurface k = −10.2252 A₂ = 0 A₄ = 0 A₆ = 3.2236 × 10⁻⁶ A₈ = −5.3588 ×10⁻⁸ A₁₀ = 0 Third surface k = 3.8529 A₂ = 0 A₄ = 1.8071 × 10⁻⁴ A₆ =3.8543 × 10⁻⁶ A₈ = −6.1982 × 10⁻⁸ A₁₀ = 0 Fifth surface k = −2.4081 A₂ =0 A₄ = −4.2584 × 10⁻⁴ A₆ = −2.8865 × 10⁻⁵ A₈ = −1.0370 × 10⁻⁶ A₁₀ = 0Sixth surface k = −5.4692 A₂ = 0 A₄ = −4.0486 × 10⁻⁴ A₆ = −1.6488 × 10⁻⁵A₈ = −6.8729 × 10⁻⁷ A₁₀ = 0 Seventh surface k = 0.3254 A₂ = 0 A₄ =1.8098 × 10⁻⁴ A₆ = 1.9304 × 10⁻⁵ A₈ = 5.1165 × 10⁻⁷ A₁₀ = 4.3288 × 10⁻⁸Tenth surface k = 0 A₂ = 0 A₄ = −3.6619 × 10⁻⁴ A₆ = −1.7580 × 10⁻⁵ A₈ =−1.2817 × 10⁻⁷ A₁₀ = 0 Twelfth surface k = 0 A₂ = 0 A₄ = −2.5932 × 10⁻⁴A₆ = 4.3267 × 10⁻⁶ A₈ = 0 A₁₀ = 0 Refractive indices classified bywavelengths in medium constituting negative lens L_(AN) nd = 1.583126 nC= 1.580139 nF = 1.589960 ng = 1.595297 nh = 1.599721 Refractive indicesclassified by wavelengths in medium constituting positive lens L_(AP) nd= 1.709995 nC = 1.697485 nF = 1.744813 ng = 1.781729 nh = 1.820349 Zoomdata (when D0 (distance from object to first surface) is infinite)Wide-angle Middle Telephoto F 6.41984 11.01046 18.48745 fno 2.13082.6883 3.5779 D0 ∞ ∞ ∞ D3 14.77590 6.40215 1.62729 D9 1.77131 3.834887.44342 D11 2.34515 3.70635 5.10940 D13 3.98433 4.12060 4.02033 D170.49902 0.50111 0.50375

Embodiment 3

FIGS. 5A, 5B, and 5C are sectional views showing optical arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, in infinite object point focusing of Embodiment3 of the zoom optical system according to the present invention. FIGS.6A-6D, 6E-6H, and 6I-6L are diagrams showing aberration characteristicsat wide-angle, middle, and telephoto positions, respectively, ininfinite object point focusing of the zoom optical system of FIGS.5A-5C. In FIG. 5A, again, reference symbol I denotes the imaging surfaceof a CCD that is an electronic image sensor, S denotes an aperture stop,FL denotes a plane-parallel plate-shaped filter, and CG denotes aplane-parallel plate-shaped CCD cover glass.

The zoom optical system of Embodiment 3 has the lens units, the filterFL, the cover glass CG, and the CCD. The zoom optical system comprises,in order from the object side, a first lens unit G1 as the lens unit A,the aperture stop S, a second lens unit G2 as the lens unit B, a thirdlens unit G3 as the lens unit C, and a fourth lens unit G4 as the lensunit D.

The first lens unit G1 includes a cemented lens in which a biconcavelens L11 and a positive meniscus lens L12 with a convex surface facingthe object side are cemented, and is constructed with a negative lenscomponent as a whole. The positive meniscus lens L12 with the convexsurface facing the object side is a lens using energy curing resin andis configured on the biconcave lens L11. The second lens unit G2includes a biconvex lens L21 and a cemented lens in which a biconvexlens L22 and a biconcave lens L23 are cemented. The third lens unit G3includes a biconcave lens L31. The fourth lens unit G4 includes abiconvex lens L41.

When the magnification is changed in the range from the wide-angleposition to the telephoto position, the first lens unit G1 is moved backand forth along the optical axis in such a way that the first lens unitG1 is initially moved toward the image side and then is moved toward theobject side. The second lens unit G2 is simply moved, together with theaperture stop S, along the optical axis toward the object side so thatspacing between the first lens unit G1 and the second lens unit G2 isnarrowed. The third lens unit G3 is simply moved along the optical axistoward the object side so as to widen the spacing between the third lensunit G3 and the fourth lens unit G4. The fourth lens unit G4 is movedback and forth along the optical axis in such a way that the fourth lensunit G4 is initially moved toward the object side and then is movedtoward the image side.

Subsequently, numerical data of optical members constituting the zoomoptical system of Embodiment 3 are shown below.

Numerical data 3 r₁ = −25.4905 (aspherical surface) d₁ = 0.8000 n_(d1) =1.74320 ν_(d1) = 49.34 r₂ = 8.2460 d₂ = 0.6848 n_(d2) = 1.75000 ν_(d2) =15.00 r₃ = 15.7873 (aspherical surface) d₃ = D3 r₄ = ∞ (stop) d₄ =0.3000 r₅ = 7.8777 (aspherical surface) d₅ = 1.8441 n_(d5) = 1.83481ν_(d5) = 42.71 r₆ = −15.9558 (aspherical surface) d₆ = 0.0791 r₇ =9.3650 (aspherical surface) d₇ = 1.7013 n_(d7) = 1.83481 ν_(d7) = 42.71r₈ = −14.1273 d₈ = 0.4000 n_(d8) = 1.80810 ν_(d8) = 22.76 r₉ = 4.5576 d₉= D9 r₁₀ = −37.4717 (aspherical surface) d₁₀ = 0.5000 n_(d10) = 2.00000ν_(d10) = 25.00 r₁₁ = 15.5000 d₁₁ = D11 r₁₂ = 103.2252 (asphericalsurface) d₁₂ = 1.3800 n_(d12) = 1.92000 ν_(d12) = 22.00 r₁₃ = −9.6000d₁₃ = D13 r₁₄ = ∞ d₁₄ = 0.5000 n_(d14) = 1.54771 ν_(d14) = 62.84 r₁₅ = ∞d₁₅ = 0.5000 r₁₆ = ∞ d₁₆ = 0.5000 n_(d16) = 1.51633 ν_(d16) = 64.14 r₁₇= ∞ d₁₇ = D17 r₁₈ = ∞ (imaging surface) Aspherical coefficients Firstsurface k = 0.6227 A₂ = 0 A₄ = 0 A₆ = 3.3561 × 10⁻⁶ A₈ = −1.5540 × 10⁻⁹A₁₀ = 0 Third surface k = −0.5547 A₂ = 0 A₄ = −9.9336 × 10⁻⁶ A₆ = 6.6953× 10⁻⁶ A₈ = 9.6741 × 10⁻⁸ A₁₀ = 0 Fifth surface k = −1.8589 A₂ = 0 A₄ =−3.2115 × 10⁻⁴ A₆ = −2.1569 × 10⁻⁵ A₈ = −9.0860 × 10⁻⁷ A₁₀ = 0 Sixthsurface k = −8.6329 A₂ = 0 A₄ = −3.5000 × 10⁻⁴ A₆ = −9.1033 × 10⁻⁶ A₈ =−7.6128 × 10⁻⁷ A₁₀ = 0 Seventh surface k = 0.1074 A₂ = 0 A₄ = 1.4490 ×10⁻⁴ A₆ = 1.5895 × 10⁻⁵ A₈ = 7.9815 × 10⁻⁷ A₁₀ = 4.1284 × 10⁻⁹ Tenthsurface k = 0 A₂ = 0 A₄ = −4.3432 × 10⁻⁴ A₆ = −3.9156 × 10⁻⁵ A₈ = 1.3010× 10⁻⁶ A₁₀ = 0 Twelfth surface k = 0 A₂ = 0 A₄ = −2.1377 × 10⁻⁴ A₆ =2.2393 × 10⁻⁶ A₈ = 0 A₁₀ = 0 Refractive indices classified bywavelengths in medium constituting negative lens L_(AN) nd = 1.743198 nC= 1.738653 nF = 1.753716 ng = 1.762047 nh = 1.769040 Refractive indicesclassified by wavelengths in medium constituting positive lens L_(AP) nd= 1.749995 nC = 1.736707 nF = 1.786700 ng = 1.822303 nh = 1.857180 Zoomdata (when D0 (distance from object to first surface) is infinite)Wide-angle Middle Telephoto F 6.41996 11.01015 18.48954 fno 2.30742.9164 3.9965 D0 ∞ ∞ ∞ D3 13.62838 6.55176 2.97274 D9 1.84065 4.010717.85352 D11 2.85247 3.85195 5.22392 D13 3.98922 4.31057 3.46097 D170.50005 0.49998 0.49996

Embodiment 4

FIGS. 7A, 7B, and 7C are sectional views showing optical arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, in infinite object point focusing of Embodiment4 of the zoom optical system according to the present invention. FIGS.8A-8D, 8E-8H, and 8I-8L are diagrams showing aberration characteristicsat wide-angle, middle, and telephoto positions, respectively, ininfinite object point focusing of the zoom optical system of FIGS.7A-7C. In FIG. 7A, again, reference symbol I denotes the imaging surfaceof a CCD that is an electronic image sensor, S denotes an aperture stop,FL denotes a plane-parallel plate-shaped filter, and CG denotes aplane-parallel plate-shaped CCD cover glass.

The zoom optical system of Embodiment 4 has the lens units, the filterFL, the cover glass CG, and the CCD. The zoom optical system comprises,in order from the object side, a first lens unit G1 as the lens unit A,the aperture stop S, a second lens unit G2 as the lens unit B, a thirdlens unit G3 as the lens unit C, and a fourth lens unit G4 as the lensunit D.

The first lens unit G1 includes a cemented lens in which a biconcavelens L11 and a positive meniscus lens L12 with a convex surface facingthe object side are cemented, and is constructed with a negative lenscomponent as a whole. The positive meniscus lens L12 with the convexsurface facing the object side is a lens using energy curing resin andis configured on the biconcave lens L11. The second lens unit G2includes a biconvex lens L21 and a cemented lens in which a biconvexlens L22, a biconcave lens L23, and a negative meniscus lens L24 with aconvex surface facing the object side are cemented. The third lens unitG3 includes a biconcave lens L31. The fourth lens unit G4 includes abiconvex lens L41.

When the magnification is changed in the range from the wide-angleposition to the telephoto position, the first lens unit G1 is moved backand forth along the optical axis in such a way that the first lens unitG1 is initially moved toward the image side and then is moved toward theobject side. The second lens unit G2 is simply moved, together with theaperture stop S, along the optical axis toward the object side so as tonarrow spacing between the first lens unit G1 and the second lens unitG2. The third lens unit G3 is simply moved toward the image side, andthe fourth lens unit G4 is simply moved toward the image side so as tokeep the spacing between the third lens unit G3 and the fourth lens unitG4 constant.

Subsequently, numerical data of optical members constituting the zoomoptical system of Embodiment 4 are shown below.

Numerical data 4 r₁ = −12.4638 (aspherical surface) d₁ = 0.8000 n_(d1) =1.49700 ν_(d1) = 81.54 r₂ = 13.3687 d₂ = 0.4776 n_(d2) = 1.63494 ν_(d2)= 23.22 r₃ = 27.4986 (aspherical surface) d₃ = D3 r₄ = ∞ (stop) d₄ =0.3000 r₅ = 7.4744 (aspherical surface) d₅ = 1.9063 n_(d5) = 1.83481ν_(d5) = 42.71 r₆ = −21.4110 (aspherical surface) d₆ = 0.0791 r₇ =11.1522 d₇ = 1.7145 n_(d7) = 1.81600 ν_(d7) = 46.62 r₈ = −11.6979 d₈ =0.4000 n_(d8) = 1.76182 ν_(d8) = 26.52 r₉ = 6.0000 d₉ = 0.1000 n_(d9) =1.63494 ν_(d9) = 23.22 r₁₀ = 3.7931 (aspherical surface) d₁₀ = D10 r₁₁ =−18.5300 (aspherical surface) d₁₁ = 0.5000 n_(d11) = 1.49700 ν_(d11) =81.54 r₁₂ = 43.8425 d₁₂ = D12 r₁₃ = 49.7881 (aspherical surface) d₁₃ =1.5213 n_(d13) = 1.83481 ν_(d13) = 42.71 r₁₄ = −9.3000 d₁₄ = D14 r₁₅ = ∞d₁₅ = 0.5000 n_(d15) = 1.54771 ν_(d15) = 62.84 r₁₆ = ∞ d₁₆ = 0.5000 r₁₇= ∞ d₁₇ = 0.5000 n_(d17) = 1.51633 ν_(d17) = 64.14 r₁₈ = ∞ d₁₈ = D18 r₁₉= ∞ (imaging surface) Aspherical coefficients First surface k = −6.4093A₂ = 0 A₄ = 0 A₆ = 1.6769 × 10⁻⁶ A₈ = −2.3120 × 10⁻⁸ A₁₀ = 0 Thirdsurface k = −2.4919 A₂ = 0 A₄ = 1.9423 × 10⁻⁴ A₆ = 1.8515 × 10⁻⁶ A₈ =−3.3639 × 10⁻⁸ A₁₀ = 0 Fifth surface k = −0.9686 A₂ = 0 A₄ = −3.9412 ×10⁻⁵ A₆ = 0 A₈ = 0 A₁₀ = 0 Sixth surface k = −70.1334 A₂ = 0 A₄ = 1.1578× 10⁻⁵ A₆ = 0 A₈ = 0 A₁₀ = 0 Tenth surface k = 0 A₂ = 0 A₄ = −2.1909 ×10⁻³ A₆ = 8.0659 × 10⁻⁵ A₈ = −9.4134 × 10⁻⁶ A₁₀ = 0 Eleventh surface k =0 A₂ = 0 A₄ = −5.4322 × 10⁻⁴ A₆ = 1.0884 × 10⁻⁵ A₈ = 0 A₁₀ = 0Thirteenth surface k = 0 A₂ = 0 A₄ = −3.4682 × 10⁻⁴ A₆ = 0 A₈ = 0 A₁₀ =0 Refractive indices classified by wavelengths in medium constitutingnegative lens L_(AN) nd = 1.496999 nC = 1.495136 nF = 1.501231 ng =1.504507 nh = 1.507205 Refractive indices classified by wavelengths inmedium constituting positive lens L_(AP) nd = 1.634940 nC = 1.627290 nF= 1.654640 ng = 1.672913 nh = 1.689873 Zoom data (when D0 (distance fromobject to first surface) is infinite) Wide-angle Middle Telephoto F6.42000 11.01030 18.48960 fno 1.8487 2.4557 3.3920 D0 ∞ ∞ ∞ D3 14.823907.08722 2.38201 D10 1.92800 6.27359 11.86067 D12 2.07054 2.07054 2.07054D14 3.37860 2.55161 1.60000 D18 0.50009 0.50001 0.49964

Embodiment 5

FIGS. 9A, 9B, and 9C are sectional views showing optical arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, in infinite object point focusing of Embodiment5 of the zoom optical system according to the present invention. FIGS.10A-10D, 10E-10H, and 10I-10L are diagrams showing aberrationcharacteristics at wide-angle, middle, and telephoto positions,respectively, in infinite object point focusing of the zoom opticalsystem of FIGS. 9A-9C. In FIG. 9A, again, reference symbol I denotes theimaging surface of a CCD that is an electronic image sensor, S denotesan aperture stop, FL denotes a plane-parallel plate-shaped filter, andCG denotes a plane-parallel plate-shaped CCD cover glass.

The zoom optical system of Embodiment 5 has the lens units, the filterFL, the cover glass CG, and the CCD. The zoom optical system comprises,in order from the object side, a first lens unit G1 as the lens unit A,the aperture stop S, a second lens unit G2 as the lens unit B, a thirdlens unit G3 as the lens unit C, and a fourth lens unit G4 as the lensunit D.

The first lens unit G1 includes a cemented lens in which a biconcavelens L11 and a positive meniscus lens L12 with a convex surface facingthe object side are cemented, and is constructed with a negative lenscomponent as a whole. The positive meniscus lens L12 with the convexsurface facing the object side is a lens using energy curing resin andis configured on the biconcave lens L11. The second lens unit G2includes a biconvex lens L21 and a cemented lens in which a biconvexlens L22 and a biconcave lens L23 are cemented. The third lens unit G3includes a biconcave lens L31. The fourth lens unit G4 includes abiconvex lens L41.

When the magnification is changed in the range from the wide-angleposition to the telephoto position, the first lens unit G1 is moved backand forth along the optical axis in such a way that the first lens unitG1 is initially moved toward the image side and then is moved toward theobject side. The second lens unit G2 is simply moved, together with theaperture stop S, along the optical axis toward the object side so as tonarrow spacing between the first lens unit G1 and the second lens unitG2. The third lens unit G3 is moved back and forth along the opticalaxis in such a way that the third lens unit G3 is initially moved towardthe image side to narrow the spacing between the third lens unit G3 andthe fourth lens unit G4 and then is moved toward the object side. Thefourth lens unit G4 is simply moved along the optical axis toward theimage side.

Subsequently, numerical data of optical members constituting the zoomoptical system of Embodiment 5 are shown below.

Numerical data 5 r₁ = −12.9570 (aspherical surface) d₁ = 0.8000 n_(d1) =1.52542 ν_(d1) = 55.78 r₂ = 10.4409 d₂ = 0.7032 n_(d2) = 1.63494 ν_(d2)= 23.22 r₃ = 22.2162 (aspherical surface) d₃ = D3 r₄ = ∞ (stop) d₄ =0.3000 r₅ = 8.6298 (aspherical surface) d₅ = 1.8448 n_(d5) = 1.83481ν_(d5) = 42.71 r₆ = −26.5988 (aspherical surface) d₆ = 0.0791 r₇ =7.1432 (aspherical surface) d₇ = 1.7812 n_(d7) = 1.83481 ν_(d7) = 42.71r₈ = −239.3124 d₈ = 0.4000 n_(d8) = 1.80810 ν_(d8) = 22.76 r₉ = 3.9396d₉ = D9 r₁₀ = −42.3355 (aspherical surface) d₁₀ = 0.5000 n_(d10) =1.52542 ν_(d10) = 55.78 r₁₁ = 19.6055 d₁₁ = D11 r₁₂ = 64.2346(aspherical surface) d₁₂ = 1.3800 n_(d12) = 1.83481 ν_(d12) = 42.71 r₁₃= −9.6000 d₁₃ = D13 r₁₄ = ∞ d₁₄ = 0.5000 n_(d14) = 1.54771 ν_(d14) =62.84 r₁₅ = ∞ d₁₅ = 0.5000 r₁₆ = ∞ d₁₆ = 0.5000 n_(d16) = 1.51633ν_(d16) = 64.14 r₁₇ = ∞ d₁₇ = D17 r₁₈ = ∞ (imaging surface) Asphericalcoefficients First surface k = −3.9537 A₂ = 0 A₄ = 0 A₆ = 2.4737 × 10⁻⁶A₈ = −3.9226 × 10⁻⁸ A₁₀ = 0 Third surface k = −0.9087 A₂ = 0 A₄ = 7.1688× 10⁻⁵ A₆ = 3.7777 × 10⁻⁶ A₈ = −4.9770 × 10⁻⁸ A₁₀ = 0 Fifth surface k =−1.9337 A₂ = 0 A₄ = −3.4869 × 10a⁻⁴ A₆ = −2.2526 × 10⁻⁵ A₈ = −5.7283 ×10⁻⁸ A₁₀ = 0 Sixth surface k = −5.9352 A₂ = 0 A₄ = −3.7375 × 10⁻⁴ A₆ =−6.1314 × 10⁻⁶ A₈ = −1.7507 × 10⁻⁷ A₁₀ = 0 Seventh surface k = 0.2051 A₂= 0 A₄ = 8.5095 × 10⁻⁵ A₆ = 1.8765 × 10⁻⁵ A₈ = 4.8202 × 10⁻⁷ A₁₀ =1.0705 × 10⁻⁸ Tenth surface k = 43.0913 A₂ = 0 A₄ = −2.6920 × 10⁻⁴ A₆ =−1.0679 × 10⁻⁵ A₈ = 1.0544 × 10⁻⁶ A₁₀ = 0 Twelfth surface k = 0 A₂ = 0A₄ = −4.1294 × 10⁻⁴ A₆ = 3.6637 × 10⁻⁶ A₈ = 0 A₁₀ = 0 Refractive indicesclassified by wavelengths in medium constituting negative lens L_(AN) nd= 1.525420 nC = 1.522680 nF = 1.532100 ng = 1.537050 nh = 1.540699Refractive indices classified by wavelengths in medium constitutingpositive lens L_(AP) nd = 1.634940 nC = 1.627290 nF = 1.654640 ng =1.672908 nh = 1.689873 Zoom data (when D0 (distance from object to firstsurface) is infinite) Wide-angle Middle Telephoto F 6.42000 11.0103018.48958 fno 1.8685 2.4621 3.4244 D0 ∞ ∞ ∞ D3 14.46707 7.07125 2.86615D9 2.20000 6.43367 10.48474 D11 2.41629 2.29056 3.84331 D13 3.128352.29609 1.60000 D17 0.50012 0.50001 0.49950

Embodiment 6

FIGS. 11A, 11B, and 11C are sectional views showing opticalarrangements, developed along the optical axis, at wide-angle, middle,and telephoto positions, respectively, in infinite object point focusingof Embodiment 6 of the zoom optical system according to the presentinvention. FIGS. 12A-12D, 12E-12H, and 12I-12L are diagrams showingaberration characteristics at wide-angle, middle, and telephotopositions, respectively, in infinite object point focusing of the zoomoptical system of FIGS. 11A-11C. In FIG. 11A, again, reference symbol Idenotes the imaging surface of a CCD that is an electronic image sensor,S denotes an aperture stop, FL denotes a plane-parallel plate-shapedfilter, and CG denotes a plane-parallel plate-shaped CCD cover glass.

The zoom optical system of Embodiment 6 has the lens units, the filterFL, the cover glass CG, and the CCD. The zoom optical system comprises,in order from the object side, a first lens unit G1 as the lens unit A,the aperture stop S, a second lens unit G2 as the lens unit B, a thirdlens unit G3 as the lens unit C, and a fourth lens unit G4 as the lensunit D.

The first lens unit G1 includes a cemented lens in which a biconcavelens L11 and a positive meniscus lens L12 with a convex surface facingthe object side are cemented, and is constructed with a negative lenscomponent as a whole. The positive meniscus lens L12 with the convexsurface facing the object side is a lens using energy curing resin andis configured on the biconcave lens L11. The second lens unit G2includes a biconvex lens L21 and a cemented lens in which a biconvexlens L22 and a biconcave lens L23 are cemented. The third lens unit G3includes a biconcave lens L31. The fourth lens unit G4 includes abiconvex lens L41.

When the magnification is changed in the range from the wide-angleposition to the telephoto position, the first lens unit G1 is moved backand forth along the optical axis in such a way that the first lens unitG1 is initially moved toward the image side and then is moved toward theobject side. The second lens unit G2 is simply moved, together with theaperture stop S, along the optical axis toward the object side so as tonarrow spacing between the first lens unit G1 and the second lens unitG2. The third lens unit G3 is moved back and forth along the opticalaxis in such a way that the third lens unit G3 is initially moved towardthe image side to narrow the spacing between the third lens unit G3 andthe fourth lens unit G4 and then is moved toward the object side. Thefourth lens unit G4 is simply moved along the optical axis toward theimage side.

Subsequently, numerical data of optical members constituting the zoomoptical system of Embodiment 6 are shown below.

Numerical data 6 r₁ = −14.0769 (aspherical surface) d₁ = 0.8000 n_(d1) =1.49700 ν_(d1) = 81.54 r₂ = 13.0399 d₂ = 0.4353 n_(d2) = 1.63494 ν_(d2)= 23.22 r₃ = 20.2304 (aspherical surface) d₃ = D3 r₄ = ∞ (stop) d₄ =0.3000 r₅ = 8.3137 (aspherical surface) d₅ = 1.8433 n_(d5) = 1.83481ν_(d5) = 42.71 r₆ = −28.3034 (aspherical surface) d₆ = 0.0791 r₇ =7.2890 (aspherical surface) d₇ = 1.7325 n_(d7) = 1.83481 ν_(d7) = 42.71r₈ = −234.9510 d₈ = 0.4000 n_(d8) = 1.80810 ν_(d8) = 22.76 r₉ = 3.9450d₉ = D9 r₁₀ = −66.2077 (aspherical surface) d₁₀ = 0.5000 n_(d10) =1.52542 ν_(d10) = 55.78 r₁₁ = 15.5000 d₁₁ = D11 r₁₂ = 48.9767(aspherical surface) d₁₂ = 1.3800 n_(d12) = 1.83481 ν_(d12) = 42.71 r₁₃= −9.8000 d₁₃ = D13 r₁₄ = ∞ d₁₄ = 0.5000 n_(d14) = 1.54771 ν_(d14) =62.84 r₁₅ = ∞ d₁₅ = 0.5000 r₁₆ = ∞ d₁₆ = 0.5000 n₁₆ = 1.51633 ν_(d16) =64.14 r₁₇ = ∞ d₁₇ = D17 r₁₈ = ∞ (imaging surface) Asphericalcoefficients First surface k = −1.7279 A₂ = 0 A₄ = 0 A₆ = 5.2480 × 10⁻⁶A₈ = 6.5711 × 10⁻⁸ A₁₀ = 0 Third surface k = −3.2269 A₂ = 0 A₄ = −1.3187× 10⁻⁵ A₆ = 6.6781 × 10⁻⁶ A₈ = −5.4466 × 10⁻⁸ A₁₀ = 0 Fifth surface k =−1.8346 A₂ = 0 A₄ = −3.1046 × 10⁻⁴ A₆ = −2.2024 × 10⁻⁵ A₈ = −1.4954 ×10⁻⁷ A₁₀ = 0 Sixth surface k = −5.2682 A₂ = 0 A₄ = 3.7806 × 10⁻⁴ A₆ =−3.7399 × 10⁻⁶ A₈ = −2.7381 × 10⁻⁷ A₁₀ = 0 Seventh surface k = 0.1385 A₂= 0 A₄ = 6.1956 × 10⁻⁵ A₆ = 1.9211 × 10⁻⁵ A₈ = 7.5338 × 10⁻⁷ A₁₀ = 0Tenth surface k = 0 A₂ = 0 A₄ = −5.4575 × 10⁻⁴ A₆ = 1.3347 × 10⁻⁵ A₈ = 0A₁₀ = 0 Twelfth surface k = 0 A₂ = 0 A₄ = −2.7359 × 10⁻⁴ A₆ = 0 A₈ = 0A₁₀ = 0 Refractive indices classified by wavelengths in mediumconstituting negative lens L_(AN) nd = 1.496999 nC = 1.495136 nF =1.501231 ng = 1.504506 nh = 1.507205 Refractive indices classified bywavelengths in medium constituting positive lens L_(AP) nd = 1.634940 nC= 1.627290 nF = 1.654640 ng = 1.672908 nh = 1.689873 Zoom data (when D0(distance from object to first surface) is infinite) Wide-angle MiddleTelephoto F 6.42001 11.01031 18.48963 fno 1.8421 2.4257 3.3791 D0 ∞ ∞ ∞D3 14.83968 7.18523 2.75812 D9 1.89368 6.35451 10.50890 D11 2.485632.12545 3.45724 D13 3.31078 2.34496 1.59995 D17 0.50015 0.50001 0.49931

Subsequently, corresponding parameter values in individual embodimentsof the present invention described above are shown in Table 1.

TABLE 1 Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5Embodiment 6 fw 6.42002 6.41984 6.41966 6.42000 6.42000 6.42001 y₁₀ 3.63.6 3.6 3.6 3.6 3.6 d_(CD)/fw 0.3719 0.3653 0.4443 0.3225 0.3764 0.3872Z_(AF) (4.494) −0.70327 −0.56446 −0.37389 −0.69299 −0.70637 −0.67222Z_(AC) (4.494) 0.78934 0.76173 1.33221 0.77798 1.01666 0.79887 Z_(AR)(4.494) 0.51930 0.53794 0.71270 0.45251 0.50704 0.52671 |Z_(AR) (h) −Z_(AC) (h)|/tp 0.6373 0.6367 0.9047 0.6815 0.7247 0.6252 *value at h =4.494 tp/tn 0.5296 0.4394 0.8560 0.5970 0.8790 0.5441 k_(AF) −2.8817−10.2252 0.6227 −6.4093 −3.9537 −1.7279 k_(AR) −2.9323 3.8529 −0.5547−2.4919 −0.9087 −3.2269 Z_(AF) (h)/Z_(AR) (h) −1.3543 −1.0493 −0.5246−1.5314 −1.3931 −1.2763 *value at h = 4.494 νdp 23.22 15.00 15.00 23.2223.22 23.22 θgFp 0.7001 0.7800 0.7122 0.6679 0.6679 0.6679 βp 0.73790.8045 0.7369 0.7057 0.7057 0.7057 θhgp 0.6765 0.8160 0.6976 0.62030.6203 0.6203 βhgp 0.7287 0.8498 0.7314 0.6725 0.6725 0.6725 ndp 1.634941.70999 1.75000 1.63494 1.63494 1.63494 νdn 81.54 59.38 49.34 81.5481.54 81.54 θgFn 0.5386 0.5438 0.5528 0.5373 0.5373 0.5373 θhgn 0.44170.4501 0.4638 0.4428 0.4428 0.4428 ndn 1.49700 1.58913 1.74320 1.497001.49700 1.49700 θgFp − θgFn 0.1615 0.2362 0.1594 0.1306 0.1306 0.1306θhgp − θhgn 0.2348 0.3659 0.2338 0.1775 0.1775 0.1775 νdp − νdn −58.32−44.38 −34.34 −58.32 −58.32 −58.32 y₀₇ 2.52 2.52 2.52 2.52 2.52 2.52 tanω_(07w) 0.41890 0.41843 0.41853 0.41919 0.41863 0.41984 (R_(CF) +R_(CR))/(R_(CF) − R_(CR)) 0.2041 0.5509 0.4148 −0.4058 0.3670 0.6206(R_(DF) + R_(DR))/(R_(DF) − R_(DR)) 0.7383 0.8370 0.8298 0.6852 0.74000.6665 y₀₇ 2.52 2.52 2.52 2.52 2.52 2.52 tan ω_(07w) 0.41890 0.418430.41853 0.41919 0.41863 0.41984 _(AVE)nd_(2P) 1.83481 1.83481 1.834811.83481 1.83481 1.83481 _(AVE)νd_(2N) 24.00 23.00 23.00 24.87 22.7622.76 nd_(4P) 1.83481 1.90000 1.90000 1.83481 1.83481 1.83481 νd_(4P)42.71 27.00 27.00 42.71 42.71 42.71

The zoom optical system of the present invention described above can beused in a photographing apparatus for photographing the image of theobject through the electronic image sensor, such as a CCD or CMOS,notably in a digital camera and a video camera, and in a personalcomputer, a telephone, and a mobile terminal, particularly in a mobilephone that is handy to carry, which are examples of informationprocessing apparatuses. What follows is a description of an example ofthe digital camera as its aspect.

FIGS. 13-15 show a digital camera incorporating the imaging opticalsystem according to the present invention in a photographing opticalsystem 41. FIG. 13 is a front perspective view showing the appearance ofa digital camera 40. FIG. 14 is a rear perspective view showing thedigital camera. FIG. 15 is a sectional view showing the opticalstructure of the digital camera 40.

The digital camera 40, in this example, includes the photographingoptical system 41 having a photographing optical path 42, a finderoptical system 43 having a finder optical path 44, a shutter button 45,a flash lamp 46, and a liquid crystal display monitor 47.

When a photographer pushes the shutter button 45 provided on the upperface of the camera 40, photographing is performed, in association withthis shutter operation, through the photographing optical system 41, forexample, the zoom optical system of Embodiment 1.

An image of an object produced by the photographing optical system 41 isformed on the imaging surface of a CCD 49. The image of the objectreceived by the CCD 49 is displayed as an electronic image on the liquidcrystal display monitor 47 provided on the back face of the camera,through an image processing means 51. A memory is placed in the imageprocessing means 51 so that a photographed electronic image can also berecorded. Also, the memory may be provided to be independent of theimage processing means 51 or may be constructed so that the image iselectronically recorded and written by a floppy (a registered trademark)disk, memory card, or MO.

Further, a finder objective optical system 53 is located on the finderoptical path 44. The finder objective optical system 53 includes a coverlens 54, a first prism 10, an aperture stop 2, a second prism 20, and afocusing lens 66. The image of the object is produced on an imagingsurface 67 by the finder objective optical system 53. The image of theobject is formed on a field frame 57 of a Porro prism 55 that is animage erecting member. Behind the Porro prism 55 is located an eyepieceoptical system 59 that introduces an erected image into an observer'seye E.

According to the digital camera 40 constructed as mentioned above, it ispossible to realize the electronic imaging apparatus having the zoomoptical system in which the number of constituents of the photographingoptical system 41 is reduced and the small-sized and slim design isachieved.

The present invention is favorable to the fields of the zoom opticalsystem suitable for an electronic imaging optical system that needs tosatisfy the slim design, high imaging performance, and the largeaperture ratio at the same time so that an object can be clearlyphotographed even in surroundings in which the amount of light is small,and of the electronic imaging apparatus having this zoom optical system.

1. A zoom optical system comprising, in order from an object side: alens unit A with negative refracting power, including onebiconcave-shaped lens component; a lens unit B with positive refractingpower; a lens unit C with negative refracting power; and a lens unit Dwith positive refracting power, wherein when a magnification of the zoomoptical system is changed, relative distances between individual lensunits are varied and the zoom optical system satisfies the followingcondition:0.2≦d _(CD) /fw≦1.2 where d_(CD) is spacing between the lens unit C andthe lens unit D on the optical axis in infinite focusing at a wide-angleposition and fw is a focal length of an entire system of the zoomoptical system at the wide-angle position.
 2. A zoom optical systemaccording to claim 1, wherein the lens unit A includes a cemented lenscomponent of a positive lens L_(AP) and a negative lens L_(AN), and thepositive lens L_(AP) is made of energy curing resin and is configureddirectly on the negative lens L_(AN).
 3. A zoom optical system accordingto claim 1 or 2, wherein the cemented lens component of the lens unit Aincludes, in order from the object side, the negative lens L_(AN) andthe positive lens L_(AP).
 4. A zoom optical system according to claim 1or 2, wherein when z is taken as a coordinate in a direction of theoptical axis, h is taken as a coordinate normal to the optical axis, krepresents a conic constant, A₄, A₆, A₈, and A₁₀ represent asphericalcoefficients, R represents a radius of curvature of a sphericalcomponent on the optical axis, and a configuration of an asphericalsurface is expressed by the following equation: $\begin{matrix}{z = {\frac{h^{2}}{R\left\lbrack {1 + \left\{ {1 - {\left( {1 + k} \right){h^{2}/R^{2}}}} \right\}^{1/2}} \right\rbrack} + {A_{4}h^{4}} + {A_{6}h^{6}} + {A_{8}h^{8}} + {A_{10}h^{10}} + \ldots}} & (a)\end{matrix}$ the zoom optical system satisfies the following condition:0.1≦|z _(AR)(h)−z _(AC)(h)/tp≦0.96 where z_(AC) is a shape of acementation-side surface, according to Equation (a), of the positivelens L_(AP); z_(AR) is a shape of an air-contact-side surface, accordingto Equation (a), of the positive lens L_(AP); h is expressed by h=0.7 fwwhen the focal length of the entire system of the zoom optical system atthe wide-angle position is denoted by fw; tp is a thickness, measuredalong the optical axis, of the positive lens L_(AP), and always Z (0)=0.5. A zoom optical system according to claim 1 or 2, wherein when z istaken as a coordinate in a direction of the optical axis, h is taken asa coordinate normal to the optical axis, k represents a conic constant,A₄, A₆, A₈, and A₁₀ represent aspherical coefficients, R represents aradius of curvature of a spherical component on the optical axis, and aconfiguration of an aspherical surface is expressed by the followingequation: $\begin{matrix}{z = {\frac{h^{2}}{R\left\lbrack {1 + \left\{ {1 - {\left( {1 + k} \right){h^{2}/R^{2}}}} \right\}^{1/2}} \right\rbrack} + {A_{4}h^{4}} + {A_{6}h^{6}} + {A_{8}h^{8}} + {A_{10}h^{10}} + \ldots}} & (a)\end{matrix}$ the zoom optical system satisfies the followingconditions:−50≦k _(AF)≦10−20≦k _(AR)≦20 and further satisfies the following condition:−8≦z _(AF)(h)/z _(AR)(h)≦2 where k_(AF) is a k value relative to a mostobject-side surface of the lens unit A and k_(AR) is a k value relativeto a most image-side surface of the lens unit A, each of which is a kvalue in Equation (a); z_(AF) is a shape of the most object-side surfaceof the lens unit A; z_(AR) is a shape of the most image-side surface ofthe lens unit A; and h is expressed by h=0.7 fw when the focal length ofthe entire system of the zoom optical system at the wide-angle positionis denoted by fw.
 6. A zoom optical system according to claim 1 or 2,wherein a refractive index ndp of the positive lens L_(AP), relative tothe d line, satisfies the following condition:1.50≦ndp≦1.85
 7. A zoom optical system according to claim 1 or 2,wherein when the magnification is changed in a range from the wide-angleposition to a telephoto position, the lens unit A is moved back andforth along the optical axis in such a way that the lens unit A isinitially moved toward an image side.
 8. A zoom optical system accordingto claim 1 or 2, wherein the lens unit B includes two lens components, asingle lens component and a cemented lens component, or three lenses. 9.A zoom optical system according to claim 1 or 2, wherein the negativelens unit C and the positive lens unit D in which a mutual spacing isvariable are arranged on an image side of the lens unit B.
 10. A zoomoptical system according to claim 9, wherein the lens unit C includes anegative lens alone and the lens unit D includes a positive lens alone.11. A zoom optical system according to claim 1 or 2, wherein a distancealong the optical axis between the lens unit A and the lens unit B isvaried for a purpose of changing the magnification; a negative lenscomponent of the lens unit A includes a cemented lens of the positivelens L_(AP) and the negative lens L_(AN); and in an orthogonalcoordinate system in which an axis of abscissas is taken as vdp and anaxis of ordinates is taken as θgFp, when a straight line expressed byθgFp=αp×vdp+βp(where αp=−0.00163) is set, vdp and θgFp of the positivelens L_(AP) are contained in both a region defined by a straight line ina lower limit of Condition (a) described below and by a straight line inan upper limit of Condition (a) and a region defined by Condition (b)described below:0.6400<βp<0.9000  (a)3<vdp<27  (b) where θgFp is a partial dispersion ratio (ng−nF)/(nF−nC)of the positive lens L_(AP), vdp is an Abbe's number (nd−1)/(nF−nC) ofthe positive lens L_(AP), nd is a refractive index relative to the dline, nC is a refractive index relative to the C line, nF is arefractive index relative to the F line, and ng is a refractive indexrelative to the g line.
 12. A zoom optical system according to claim 11,wherein in an orthogonal coordinate system in which an axis of abscissasis taken as vdp and an axis of ordinates is taken as θhgp, when astraight line expressed byθhgp=αhgp×vdp+βhgp(where αhgp=−0.00225) is set, vdp and θhgp of thepositive lens L_(AP) are contained in both a region defined by astraight line in a lower limit of Condition (a) described below and by astraight line in an upper limit of Condition (a) and a region defined byCondition (b) described below.0.5700<βhgp<0.9500  (a)3<vdp<27  (b) where θhgp is a partial dispersion ratio (nh−ng)/(nF−nC)of the positive lens L_(AP), vdp is an Abbe's number (nd−1)/(nF−nC) ofthe positive lens L_(AP), nd is a refractive index relative to the dline, nC is a refractive index relative to the C line, nF is arefractive index relative to the F line, ng is a refractive indexrelative to the g line, and nh is a refractive index relative to the hline.
 13. A zoom optical system according to claim 11 or 12, furthersatisfying the following condition:0.08≦θgFp−θgFn≦0.50 where θgFp is a partial dispersion ratio(ng−nF)/(nF−nC) of the positive lens L_(AP), θgFn is a partialdispersion ratio (ng−nF)/(nF−nC) of the negative lens L_(AN), nC is arefractive index relative to the C line, nF is a refractive indexrelative to the F line, and ng is a refractive index relative to the gline.
 14. A zoom optical system according to claim 13, furthersatisfying the following condition:0.09≦θhgp−θhgn≦0.60 where θhgp is a partial dispersion ratio(nh−ng)/(nF−nC) of the positive lens L_(AP), θhgn is a partialdispersion ratio (nh−ng)/(nF−nC) of the negative lens L_(AN), nC is arefractive index relative to the C line, nF is a refractive indexrelative to the F line, ng is a refractive index relative to the g line,and nh is a refractive index relative to the h line.
 15. A zoom opticalsystem according to claim 13 or 14, further satisfying the followingcondition:vdp−vdn≦−30 where vdp is an Abbe's number (nd−1)/(nF−nC) of the positivelens L_(AP), vdn is an Abbe's number (nd−1)/(nF−nC) of the negative lensL_(AN), nd is a refractive index relative to the d line, nC is arefractive index relative to the C line, and nF is a refractive indexrelative to the F line.
 16. An electronic imaging apparatus having azoom optical system, the electronic imaging apparatus comprising: a zoomoptical system; and an electronic imaging unit that has an electronicimage sensor in the proximity of an imaging position of the zoom opticalsystem so that an image formed through the zoom optical system is pickedup by the electronic image sensor and image data picked up by theelectronic image sensor are electrically processed and can be output asimage data whose format is changed, wherein the zoom optical system is azoom optical system according to claim 1 or 2 and in nearly infiniteobject point focusing, satisfies the following condition:0.7<y ₀₇/(fw·tan ω_(07w))<0.94 where y₀₇ is expressed by y₀₇=0.7y₁₀ wheny₁₀ denotes a distance from a center to a point farthest from the center(the maximum image height) within an effective imaging surface (animageable surface) of the electronic image sensor, ω_(07w) is an anglemade by a direction of an object point corresponding to an image point,connecting the center of the imaging surface at the wide-angle positionand a position of the image height you, with the optical axis, and fw isa focal length of an entire system of the zoom optical system at thewide-angle position.